Moldable charger with shape-sensing means for an implantable pulse generator

ABSTRACT

Electrical energy is transcutaneously transmitted from an external charger to an implanted medical device. The external charger includes a charging head that is selectively shapeable to conform to the surface of a patient to enhance charge efficiency and patient comfort. An alternating current charging coil is housed in the charging head and configured for transcutaneously transmitting electrical energy to the implanted medical device. The shape of the coil is changeable as the charging head is shaped, and at least one sensor determines changes in the shape of the charging coil and causes the charge of the coil to be adjusted based on the coil shape.

FIELD OF THE INVENTION

The present invention relates to external charging devices forimplantable devices, and more particularly, to devices fortranscutaneously recharging devices implanted within patients.

BACKGROUND OF THE INVENTION

Implantable stimulation devices are devices that generate and deliverelectrical stimuli to body nerves and tissues for the therapy of variousbiological disorders, such as: pacemakers to treat cardiac arrhythmia;defibrillators to treat cardiac fibrillation; cochlear stimulators totreat deafness; retinal stimulators to treat blindness; musclestimulators to produce coordinated limb movement; spinal cordstimulators to treat chronic pain; cortical and deep brain stimulatorsto treat motor and psychological disorders; and other neural stimulatorsto treat urinary incontinence, sleep apnea, shoulder sublaxation, etc.The present invention may find applicability in all such applications,although the description that follows will generally focus on the use ofthe invention within a spinal cord stimulation system, such as thatdisclosed in U.S. Pat. No. 6,516,227 (“the '227 patent”), issued Feb. 4,2003 in the name of inventors Paul Meadows et al., which is incorporatedherein by reference in its entirety.

As an alternative to having a lead or wire pass through the skin of thepatient, power and/or data can be supplied to an implanted medicaldevice via an RF or electromagnetic link that couples power from anexternal (non-implanted) coil to an internal (implanted) coil. So longas a suitable link, e.g., an inductive link, is established betweenthese two coils, which means some sort of external power source must becarried by or worn by the patient, power and/or data can be continuouslysupplied to the implanted medical device from the worn or carriedexternal device, thereby allowing the implanted medical device toperform its intended function.

It is also known to power an implanted medical device with a batterythat is housed internal to the implanted device. However, any batteryused for extended periods of time will eventually need to be eitherrecharged or replaced. Replacing an internally implanted battery maysubject the patient to further surgery and thus is not desirable, atleast not on a frequent basis.

Rather than replace an implanted battery, the battery can be rechargedby transcutaneously coupling power from an external source to animplanted receiver that is connected to the battery. Although power canbe coupled from an external source at radio frequencies using matchingantennas, it is generally more efficient to employ an externaltransmission coil and an internal receiving coil which are inductively(electromagnetically) coupled to each other to transfer power at lowerfrequencies. In this approach, the external transmission coil isenergized with alternating current (AC), producing a varying magneticflux that passes through the patient's skin and induces a correspondingAC voltage in the internal receiving coil. The voltage induced in thereceiving coil may then be rectified and used to power the implanteddevice and/or to charge a battery or other charge storage device (e.g.,an ultracapacitor), which in turn powers the implanted device. Forexample, U.S. Pat. No. 4,082,097 discloses a system for charging arechargeable battery in an implanted human tissue stimulator by means onan external power source.

To allow for flexibility of use and increased comfort to a patient asthe implanted battery is charged, the patient would benefit from aconvenient unobtrusive external charging device that transmits powertranscutaneously to an implanted device, wherein such external chargingdevice is not only small and lightweight, but is also readilyconformable to the patient in close proximity to the implanted device.For example, the device could be constructed such that it could beformed to any shape when needed, or the device could be constructed tobe shaped in one particular form and then remain in that form forfrequent use on the same area of the patient.

In shaping such an external charging device to fit the patient, it isalso important to consider the shape of the charging coil in theexternal charging device. In particular, if the shape of the chargingcoil in the external charging device changes as the external chargingdevice is shaped to conform to the patient, the characteristics of thecharge from the charging coil may change, possibly negatively impactingthe coupling factor of the external charging device and the IPG and thusthe efficiency of the charging action. Not only does good couplingincrease the power transferred from the external charger to theimplantable pulse generator, it also minimizes heating in theimplantable pulse generator. This in turn reduces the power requirementsof the external charger, which reduces heating of the external chargerand minimizes the smaller form factor of the external charger. As such,maintaining good coupling may be achieved by monitoring any change inthe shape of the coil and subsequently adjusting power requirements ofthe external charger.

Thus, there remains a need for improved devices and methods forshapeable devices that conform to a surface of the patient while alsoensuring that changes in the shape of the charging coil do notnegatively impact the charging action of the implanted device.

SUMMARY OF THE INVENTION

In accordance with the present invention, an external charger for animplantable medical device is provided. The external charger comprises acharging head that is selectively shapeable to conform to a surface of apatient. The external charger also comprises an alternating current (AC)charging coil housed in the body and configured for transcutaneouslytransmitting electrical energy to the implanted medical device, whereinthe shape of the coil is changeable as the body is shaped. The externalcharger further comprises at least one sensor, such as a strain gauge,for determining the shape of the coil. In one embodiment, the externalcharger further comprises a processor configured to adjust the charge ofthe coil in response to receiving signals from the sensor(s) regardingchanges in the shape of the coil.

In another embodiment, a method of charging an implantable medicaldevice with the external charger is provided, comprising placing theexternal charger on a surface of a patient in the general vicinity ofthe implantable device and transcutaneously transmitting energy from thecoil to the implantable medical device. Additionally, the externalcharger is shaped to conform to the surface of the patient and adheredto the patient.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is plan view of one embodiment of a spinal cord stimulation (SCS)system arranged in accordance with the present inventions;

FIG. 2 is a plan view of the SCS system of FIG. 1 in use with a patient;

FIG. 3 is a perspective view of an external charger used in the SCSsystem;

FIG. 4 is a block diagram of the internal components of one embodimentof an external charger and implantable pulse generator used in the SCSsystem of FIG. 1;

FIGS. 5A and 5B are perspective views with cut-outs of one embodiment ofa charging head used in the SCS system of FIG. 1;

FIGS. 6A and 6B are perspective views with cut-outs of alternativeembodiments of the charging head shown in FIGS. 5A and 5B;

FIGS. 7A and 7B are perspective views of another alternative embodimentof the charging head shown in FIGS. 5A and 5B;

FIGS. 8A and 8B are perspective views of another alternative embodimentof a charging head, featuring a curable material, used in the SCS systemof FIG. 1;

FIGS. 9A-9F are perspective views with cut-outs of another alternativeembodiment of a charging head, featuring a plurality of hinged sections,used in the SCS system of FIG. 1;

FIG. 10 is a perspective view of an alternative embodiment of thecharging head shown in FIGS. 9A-9F;

FIG. 11 is a flow diagram of a method used by the external charger tocharge the implantable pulse generator.

FIGS. 12 and 13 are perspective views of a method of using the externalcharger in the SCS system of FIG. 1, and in particular using thecharging head illustrated in FIGS. 5A and 5B; and

FIG. 14 is a perspective view of a method of using the external chargerin the SCS system of FIG. 1, and in particular using the charging headillustrated in FIGS. 8A-8F.

DETAILED DESCRIPTION OF THE EMBODIMENTS

At the outset, it is noted that the present invention may be used withan implantable pulse generator (IPG) or similar implanted electricalstimulator, which may be used as a component of numerous different typesof stimulation systems. The description that follows relates to a spinalcord stimulation (SCS) system. However, it is to be understood that thewhile the invention lends itself well to applications in SCS, theinvention, in its broadest aspects, may not be so limited. Rather, theinvention may be used with any type of implantable electrical circuitryused to stimulate tissue. For example, the present invention may be usedas part of a pacemaker, a defibrillator, a cochlear stimulator, aretinal stimulator, a stimulator configured to produce coordinated limbmovement, a cortical and deep brain stimulator, peripheral nervestimulator, or in any other neural stimulator configured to treaturinary incontinence, sleep apnea, shoulder sublaxation, etc.

Turning first to FIG. 1, an exemplary SCS system 10 generally comprisesan implantable neurostimulation lead 12, an implantable pulse generator(IPG) 14, an external (non-implanted) programmer 16, and an external(non-implanted) charger 18. In the illustrated embodiment, the lead 12is a percutaneous lead and, to that end, includes a plurality of in-lineelectrodes 20 carried on a flexible body 22. The IPG 14 is electricallycoupled to the lead 12 in order to direct electrical stimulation energyto each of the electrodes 20.

The IPG 14 includes an outer case formed from an electricallyconductive, biocompatible material, such as titanium. The case forms ahermetically sealed compartment wherein the electronic and othercomponents are protected from the body tissue and fluids. While aportion of the electronic components of the IPG 14 will be described infurther detail below, additional details of the IPG 14, including thebattery, antenna coil, and telemetry and charging circuitry, aredisclosed in U.S. Pat. No. 6,516,227, which is expressly incorporatedherein by reference.

As shown in FIG. 2, the neurostimulation lead 12 is implanted within theepidural space 26 of a patient through the use of a percutaneous needleor other convention technique, so as to be in close proximity to thespinal cord 28. Once in place, the electrodes 20 may be used to supplystimulation energy to the spinal cord 28 or nerve roots. The preferredplacement of the lead 12 is such that the electrodes 20 are adjacent,i.e., resting upon, the nerve area to be stimulated. The IPG 14 may beimplanted in various suitable locations of the patient's body, such asin a surgically-made pocket either in the abdomen or above the buttocks.A lead extension 30 may facilitate locating the IPG 14 away from theexit point of the lead 12.

Referring back to FIG. 1, the IPG 14 is programmed, or controlled,through the use of the external programmer 16. The external programmer16 is transcutaneously coupled to the IPG 14 through a suitablecommunications link (represented by the arrow 32) that passes throughthe patient's skin 34. Suitable links include, but are not limited toradio frequency (RF) links, inductive links, optical links, and magneticlinks. For purposes of brevity, the electronic components of theexternal programmer 16 will not be described herein. Details of theexternal programmer, including the control circuitry, processingcircuitry, and telemetry circuitry, are disclosed in U.S. Pat. No.6,516,227, which has been previously incorporated herein by reference.

The external charger 18 is transcutaneously coupled to the IPG 14through a suitable link (represented by the arrow 36) that passesthrough the patient's skin 34, thereby coupling power to the IPG 14 forthe purpose of operating the IPG 14 or replenishing a power source, suchas a rechargeable battery (e.g., a Lithium Ion battery), within the IPG14. In the illustrated embodiment, the link 36 is an inductive link;that is, energy from the external charger 18 is coupled to the batterywithin the IPG 14 via electromagnetic coupling. Once power is induced inthe charging coil in the IPG 14, charge control circuitry within the IPG14 provides the power charging protocol to charge the battery.

Once the IPG 14 has been programmed, and its power source has beencharged or otherwise replenished, the IPG 14 may function as programmedwithout the external programmer 16 or the external charger 18 beingpresent. While the external programmer 16 and external charger 18 aredescribed herein as two separate and distinct units, it should beappreciated that the functionality of the external programmer 16 andexternal charger 18 can be combined into a single unit. It should benoted that rather than an IPG, the system 10 may alternatively utilizean implantable receiver-stimulator (not shown) connected to lead 12. Inthis case, the power source, e.g., a battery, for powering the implantedreceiver, as well as control circuitry to command thereceiver-stimulator, will be contained in an external controller/chargerinductively coupled to the receiver-stimulator via an electromagneticlink.

Referring now to FIG. 3, the external components of the external charger18 will now be described. In this embodiment, the external charger 18takes the form of a two-part system comprising a portable charger 50 anda charging base station 52. The charging base station 52 includes an ACplug 54, so that it can be easily plugged into any standard 110 voltalternating current (VAC) or 200 VAC outlet. The charging base station52 further includes an AC/DC transformer 55, which provides a suitableDC voltage (e.g., 5VDC) to the circuitry within the charging basestation 52.

The portable charger 50 includes a housing 56 for containing circuitry,and in particular, the recharging circuitry and battery (not shown inFIG. 3), which will be discussed in further detail below. The housing 56is shaped and designed in a manner that allows the portable charger 50to be detachably inserted into the charging base station 52 and returnedto the charging base station 52 between uses, thereby allowing theportable charger 50, itself, to be recharged. Thus, both the IPG 14 andthe portable charger 50 are rechargeable. The portable charger 50 may bereturned to the charging base station 52 between uses. Also, theportable charger 50 may be carried on the patient, e.g., in a pouchstrapped to the patient, or placed near the patient.

In the illustrated embodiment, the portable charger 50 includes acharging head 58 connected to the housing 56 by way of a suitableflexible cable 60. For purposes of illustration, the charging head 58 isshown in this embodiment as having a curvaceous shape and is alsoflexible, more details of which will be provided below. The charginghead 58 houses an antenna 82, and in particular an AC coil 82 (see FIGS.5A and 5B), which will also be described in more detail below. The coil82 transmits the charging energy to the IPG 14. In an alternativeembodiment, the portable charger 50 does not include a separate charginghead, but instead includes a single housing that contains the rechargingcircuitry, battery, and AC coil.

Referring to FIG. 4, the recharging elements of the IPG 14 and externalcharger 18 will now be described. It should be noted that the diagram ofFIG. 4 is functional only, and is not intended to be limiting. Those ofskill in the art, given the descriptions presented herein, should beable to readily fashion numerous types of recharging circuits, orequivalent circuits, that carry out the functions indicated anddescribed.

As previously discussed above, the external charger 18 and IPG 14 areinductively coupled together through the patient's skin 34 (shown bydotted line) via the inductive link 36 (shown by wavy arrow). Theportable charger 50 includes a battery 66, which in the illustratedembodiment is a rechargeable battery, such as a Lithium Ion battery.When a recharge is needed, energy (shown by arrow 68) is coupled to thebattery 66 via the charging base station 52 in a conventional manner. Inthe illustrated embodiment, the battery 66 is fully charged inapproximately four hours. Once the battery 66 is fully charged, it hasenough energy to fully recharge the battery of the IPG 14. If theportable charger 50 is not used and left on charger base station 52, thebattery 66 will self-discharge at a rate of about 10% per month.Alternatively, the battery 66 may be a replaceable battery.

The portable charger 50 also includes: a charge controller 70, whichserves to convert the DC power from an AC/DC transformer 55 to theproper charge current and voltage for the battery 66; a batteryprotection circuit 72, which monitors the voltage and current of thebattery 66 to ensure safe operation via operation of FET switches 74,76; a fuse 78 that disconnects the battery 66 in response to anexcessive current condition that occurs over an extended period of time;a power amplifier 80, and in particular a radio frequency (RF)amplifier, for converting the DC power from the battery 66 to a largealternating current; and an electrical current detector 108 thatmeasures the magnitude of the electrical current input from the poweramplifier 80 into the coil 82, and continually outputs the measuredmagnitudes to a processor 120 as the frequency of the current is varied.Further details discussing this control and protection circuitry aredescribed in U.S. Pat. No. 6,516,227, which has been previouslyincorporated herein by reference.

As will be described in further detail below, the charging head 58 isflexible so as to be selectively shaped to conform to a patient. Toallow for such flexibility, the coil 82 may change shape as the charginghead is shaped 58. However, a change in the shape of the coil maydecrease the efficiency of energy transfer from the charging head 58 tothe IPG 14. Thus, to monitor changes in the shape of the coil 82, thecharging head 58 includes one or more sensors 118, e.g., one or morestrain gauges, in communication with the coil 82. The sensors 118 maymonitor the shape of the coil 82 on a continuous or intermittent basis,or on a discrete basis as selectively determined by manual operation(e.g., via a communication system used by medical personnel). Thesensors 118 then communicate the shape of the coil 82 to the processor120, or optionally a separate processor. The processor 120 thencommunicates directly or indirectly to the coil 82, e.g., through theamplifier 80 and/or a separate programmer, to raise or lower thefrequency of the charge delivered from the coil 82 to the IPG 14 tomaintain charge efficiency based on the changed shape of the coil 82.

For example, if the sensors 118 determine that the coil 82 is curved acertain amount as the charging head 58 is shaped, the sensors 118communicate the change in the shape of the coil 82 to the processor 120.The processor 120 then adjusts the charging frequency of the coil 82 toa value corresponding to the changed shape of the coil 82. To this end,the processor 120 may include a memory component 102 (see FIG. 4) with aprogram that correlates the shape of the coil 82 with resistance in thecoil 82 and then determines the needed adjustment in the chargingfrequency of the coil 82 to maintain an efficient charge rate of the IPG14. Other features regarding the parts, circuitry, and operation of thesensors 118 and the processor 120 are known and understood in the artand thus, for purposes of brevity, are not included here.

To further ensure efficient transfer of energy to the IPG 14, theexternal charger 18 may include a bar charge indicator (not shown)located on the portable charger 50 or on the charging head 58, whichprovides a visual indication in the form of bars of the chargingstrength between the coil 82 and the IPG 14. The bar charge indicatormay also signal to the user whether the coil 82 is properly aligned withthe IPG 14. The external charger 18 may further include a misalignmentindicator (not shown) located on the charging head 58 that provides anaudible or tactile indication when the coil 82 is misaligned relative tothe IPG 14. Alternatively, the misalignment indicator will generate anaudible or tactile indication to indicate an alignment condition onlywhen the charging head 58 is sufficiently aligned with the IPG 14. Onceproper alignment with the IPG 14 has been achieved, as indicated by thebar charge indicator or misalignment indicator, the charging head 58 maybe adhered to the patient's skin as described above. Details of the barcharge indicator and misalignment indicator are disclosed in U.S. patentapplication Ser. No. 11/748,436, which is expressly incorporated hereinby reference.

Turning to the IPG, the IPG 14 includes an antenna 84, and in particulara coil, configured for receiving the alternating current from theexternal charger 18 via the inductive coupling. The coil 84 may beidentical to, and preferably has the same resonant frequency as, thecoil 82 of the external charger 18. The IPG 14 further comprisesrectifier circuitry 86 for converting the alternating current back to DCpower. The rectifier circuitry 86 may, e.g., take the form of a bridgerectifier circuit. The IPG 14 further includes a rechargeable battery88, such as a Lithium Ion battery, which is charged by the DC poweroutput by the rectifier circuitry 86. Typically, charging of the IPG 14continues until the battery of the IPG 14 has been charged to at least80% of capacity. In the illustrated embodiment, the battery 88 can befully charged by the external charger 18 in under three hours (80%charge in two hours), at implant depths of up to 2.5 cm.

The IPG 14 also includes: a charge controller 90, which serves toconvert the DC power from the rectifier circuitry 86 to the propercharge current and voltage for the battery 88; a battery protectioncircuit 92, which monitors the voltage and current of the battery 88 toensure safe operation via operation of a FET switch 94; and a fuse 96that disconnects the battery 88 in response to an excessive currentcondition that occurs over an extended period of time. Further detailsdiscussing this control and protection circuitry are described in U.S.Pat. No. 6,516,227, which has been previously incorporated herein byreference.

Referring now to FIGS. 5A and 5B, one embodiment of the charging head 58will now be described. In this embodiment, the charging head 58 encasesthe coil 82 that is configured for transmitting the alternating currentto the IPG 14 via inductive coupling. The coil 82 may comprise a 36turn, single layer, 30 AWG copper air-core coil having a typicalinductance of 45 μH and a DC resistance of about 1.15Ω. The coil 82 maybe tuned for a resonance at 80 KHz with a parallel capacitor (notshown).

In the illustrated embodiment, the charging head 58 is formed from aflexible material that allows the charging head 58 to be selectivelyshaped as desired, e.g., by the user squeezing or bending the charginghead 58 (see FIG. 5B). In this manner, the charging head 58 is shaped toconform to a bodily surface of the patient. The material forming thecharging head 58 may, e.g., be composed of silicone, rubber,polyurethane, or a combination of these and/or similar materials.

The charging head 58 also includes a plurality of malleable supportmembers 110 (some shown in phantom) that bend as the charging head 58 isshaped. Once the charging head 58 is shaped as desired, the supportmembers 110 substantially maintain their bent form and thus helpmaintain the desired shape of the charging head 58, as shown in FIG. 5B.In other words, the support members 110 help to hold the charging head58 in a fixed configuration until a physical force is applied to changethe shape of the charging head 58.

In the illustrated embodiment, the support members 110 form longitudinalribs. In other embodiments, the support members 110 may form plates 110a (see FIG. 6A) or a mesh 110 b (see FIG. 6B). The support members 110may extend through the length of the charging head 58 or only a portionof the charging head 58. Also, the support members 110 may be formed ofaluminum, plastic, or other suitable materials that do not impede thecharging function of the external charger 18 while helping to supportand maintain the shape of the charging head 58.

The charging head 58 may also have other structures, other than theelliptical structure shown in FIGS. 5A and 5B, which allow the charginghead 58 to be bent into other shapes. For example, FIG. 7A illustratesan embodiment in which the charging head 58 has legs 59 in an X-shapedconfiguration, wherein the legs 59 can be bent toward each other, asshown in FIG. 7B. This embodiment may be particularly useful forencircling a patient's limb.

Because the charging head 58 can substantially conform to a surface ofthe patient, the efficiency with which the coil 82 charges the IPG 14may be increased, as any gaps between the charger 18 and the patient'sskin are minimized or eliminated. At the same time, the patient'scomfort is enhanced, because the charging head 58 is shaped to suit thepatient. However, as the charging head 58 is shaped, the shape of thecoil 82 may change, which in turn may affect the charging efficiency ofthe coil 82.

To address such changes in charging efficiency, the charging head 58includes the sensors 118, described above in reference to FIG. 4, tomonitor changes in the shape of the coil 82. The sensors 118 may beplaced over the coil 82 on one or both sides of the coil 82, and mayalso be affixed to the coil 82 with a suitable connector or adhesive.While the sensors 118 are illustrated on the embodiment of the chargerhead 58 shown in FIGS. 5A and 5B, the sensors 118 may also be used onthe other embodiments described herein.

Referring to FIGS. 8A and 8B, another embodiment of the charging head 58is initially formed from a flexible material that allows the charginghead 58 to be selectively shaped as desired, as described above. In thiscase, however, the flexible material can be cured afterward, byheat-setting or other processes known in the art, such that the charginghead 58 remains set in the selected shape. This embodiment may beparticularly useful when a sturdier, less flexible, i.e., morepermanent, form of the charging head 58 is desired. In one embodiment,the material forming the charging head 58 is substantially composed of athermoset plastic.

Once the charging head 58 is shaped as desired, the thermoset plastic iscured using a suitable process known in the art, such as heat-setting orexposure to ultraviolet light, wherein the thermoset plastic maintains afixed shape, as shown in FIG. 8A. In this embodiment, the thermoplasticcannot be re-cured and re-shaped and thus remains in the fixed shape. Inanother embodiment, the material forming the charging head 58 issubstantially composed of a thermoplastic. In this embodiment, once thecharging head 58 is shaped as desired, the thermoplastic is cured usinga suitable process known in the art, such as by cooling or a catalystchemical reaction. The thermoplastic maintains a fixed shape without anyadditional treatment but can later be heated, or other suitableprocesses can be used, to return the thermoplastic to a flexible state.Then, as shown in FIG. 8B, the thermoplastic can be re-shaped andre-cured to maintain a new shape as desired, which can also be donemultiple times.

Referring to FIGS. 9A-9F, another embodiment of a charging head 58includes a bendable shell 112 that can be selectively shaped. The shell122 has a plurality of hinged sections 114 that pivot against each otheras the shell 112 is bent in shaping the charging head 58. For example,the shell 112 may be bent from a flat configuration to a crescentconfiguration (FIG. 9B). The hinged sections 114 may employ any of avariety of suitable hinge mechanisms known in the art that allow thehinged sections 114 to pivot against each other while providing a widerange of movement, such as a butterfly hinge 115 a (FIG. 9C), a flushhinge 115 b (FIG. 9D), or a barrel hinge 115 c (FIG. 9E), or also ajoint assembly such as a ball and socket joint 115 d (FIG. 9F). Thehinge designs may also include gear teeth or other components known inthe art to control the hinging movement of the hinged sections 114 andto help maintain the shell 112 in a desired shape. The shell 112 may becomposed of any of a variety of suitable materials that are sufficientlyrigid to help stabilize the shell 112 without interfering with thecharging action of the external charger 18, such as plastic, ceramic, ora combination of these and/or similar materials.

As an additional feature, the shell 112 may further include a skin 116that substantially covers the outer surface of the shell 112, as shownin FIG. 10, or alternatively, the inner surface of the shell 112 or boththe inner and outer surfaces of the shell 112. The skin 116 helps toprotect the coil 82 and other electrical components in the charging head58, such that if the shell 112 is bent enough to form an open spacebetween the hinged sections 114, or if the shell 112 cracks or breaks,the electrical components remain covered. The skin 116 is preferablycomposed of one or more waterproof materials that are sufficientlyflexible to accommodate bending of the shell 112, such as plastic,rubber, polyurethane, or a combination of these and/or similarmaterials.

Having described the structure and function of the charging system, onemethod of using the external charger 18 to recharge the IPG 14 will nowbe described with reference to FIGS. 11-13. First, the charging head 58and the portable charger 50 are placed in the general vicinity of theimplanted IPG 14 (step 200), as shown in FIG. 12. Next, the portablecharger 50 is turned on (step 202), thereby transcutaneouslytransmitting charging energy from the charging head 58 to the IPG 14 tocharge the IPG 14, as described above (step 204). The proper placementof the charging head 58 is then determined (step 206) to help optimizecharging efficiency of the IPG 14. For example, in the embodimentincluding an alignment (or misalignment) indicator, audible or tactileindications from the indicator are used to determine proper alignmentbetween the charging head 58 and the IPG 14. The charging head 58 isthen shaped to conform to the surface of the patient where the charginghead 58 will be attached (step 208), as shown in FIG. 13.

In this case where the charging head 58 illustrated in FIGS. 5A and 5Bis used, the support members 110 help maintain the shape of the charginghead 58 on the patient. For the embodiment in which the material of thecharging head 58 is cured, the charging head 58 may be first shaped onthe patient, after which the material is cured, and then the charginghead 58 is returned for use on the patient. To charge the IPG 14 usingthe embodiment of the charging head 58 illustrated in FIGS. 9A and 9B,the charging head 58 is bent to conform to the patient, causing thehinged sections 114 to pivot as the charging head 58 is bent, as shownin FIG. 14.

The charging head 58 is then adhered to the patient (step 210). Thecharging head may be adhered to the patient using any suitable form ofadhesive, wherein the form of adhesive is preferably comfortable for thepatient. For example, the charging head may include double-sided medicaltape that can be added and removed as needed, or a moisture-activatedadhesive patch (not shown), wherein a small amount of liquid is appliedto the patch for adherence to the patient. The patch may be selectivelyplaced on different areas or fixed on one area of the charging head 58.Also, opposing ends of the charging head may be joined by a suitableadhesive, for example, to secure the charging head around a patient'slimb, neck, or head. The charging head may also be connected to a strap(not shown) that is secured to the patient by a snap, button, orhook-and-loop attachment, as examples, for additional support on thepatient.

The charging frequency of the energy may then be adjusted based on theshape of the coil 82 in the charging head 58. In particular, the sensors118 determine the shape of the coil 82 (step 212) and communicate anychange in shape to the processor 120 (step 214). The processor 120determines the proper charging frequency of the coil 82 to maintaincharging efficiency (step 216) and causes the coil 82 to adjust to suchfrequency (step 218). The charging frequency may be adjusted based onvalues stored in memory 102 in the processor 120. If further shaping ormovement of the charging head 58 occurs to change the coil 82 shape, thesensors 118 will determine the new shape of the coil 82 and communicatethe new shape to the processor 120, which in turn will adjust thecharging frequency of the coil 82. The charging head 58 thus continuesto charge the IPG 14 as needed, preferably until the IPG 14 is fullycharged, after which the charging head 58 is removed from the patient(step 220).

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

1. An external charger for an implantable medical device, comprising: acharging head configured for being selectively shaped to conform to asurface of a patient; an alternating current (AC) charging coil housedin the charging head and configured for transcutaneously transmittingelectrical energy to the implanted medical device, wherein the shape ofthe coil is changeable as the charging head is shaped; at least onesensor for sensing a change in the shape of the coil; and a processorthat communicates with the coil to adjust the charging frequency of thecoil in response to receiving signals from the at least one sensorregarding changes in the shape of the coil.
 2. The external charger ofclaim 1, wherein the charging head further comprises a plurality ofmalleable support members extending through the charging head foraffixing the charging head in the selected shape while the charging headconforms to the surface of the patient.
 3. The external charger of claim2, wherein the plurality of malleable support members comprises ribs. 4.The external charger of claim 2, wherein the plurality of malleablesupport members comprises plates.
 5. The external charger of claim 2,wherein the plurality of malleable support members comprises a mesh. 6.The external charger of claim 2, wherein the plurality of malleablemembers is configured to affix the charging head in the selected shapeuntil a physical force is externally applied to re-shape the charginghead.
 7. The external charger of claim 1, wherein the at least onesensor comprises a strain gauge.
 8. The external charger of claim 1,wherein the charging head has an X-shaped configuration.
 9. The externalcharger of claim 1, wherein the charging head comprises a plurality ofpivotable hinged sections integrated with an outer surface of thecharging head for selectively shaping the charging head to conform to asurface of a patient and a waterproof material substantially coveringone of an inner or outer surface of the charging head.
 10. The externalcharger of claim 1, wherein the charging head comprises a flexiblematerial that is curable to become inflexible and embody a fixed shape,and is further configured for being re-shaped and re-cured multipletimes.
 11. The external charger of claim 1, wherein the charging headcomprises a flexible material that is curable to become inflexible andembody a fixed shape, and is further configured to be cured once, afterwhich the material maintains a permanent shape and cannot be re-cured toform another shape.
 12. The external charger of claim 1, wherein theexternal charger further comprises a misalignment indicator forproviding a signal to indicate the external charger is aligned with theimplantable medical device.
 13. A method of charging an implantablemedical device, comprising: placing the external charger of claim 1 on asurface of a patient in the general vicinity of the implantable device;transcutaneously transmitting energy from the coil to the implantablemedical device; and shaping the external charger to conform to thesurface of the patient; and adhering the external charger to thepatient.
 14. The method of claim 13, further comprising aligning theexternal charger and the implantable medical device with an alignmentindicator.
 15. The method of claim 13, wherein the external charger isadhered to the patient with a moisture-activated adhesive patch.
 16. Themethod of claim 13, further comprising adjusting the charging frequencyof the coil based on a change in the shape of the coil sensed by the atleast one sensor.
 17. The method of claim 16, further comprisingcommunicating changes in the shape of the coil sensed by the at leastone sensor to the processor, wherein the processor communicates with thecoil to adjust the charging frequency of the coil based on the change inthe shape of the coil.
 18. The method of claim 1, wherein the processorcomprises a memory component that correlates the shape of the coil withresistance in the coil to determine the adjustment to the chargingfrequency of the coil.